The present invention relates to a method for providing piercing tabs on container lids, said tabs working by a leverage effect, and the lids being produced from a supple and tearable material.
Many devices are known for opening lids.
For example, lids have been proposed which comprise frangible score lines and are equipped with an element which is grasped and pulled to break the lid open along the frangible score lines. This opening system is generally awkward and requires a score line which is incompatible with the preservation of certain products (oxidation and/or bacteriological contamination, level with the base of the score lines, for example, may occur whenever the base of said line touches an oxidizable and/or nonsterile layer of a surface-sterilized multilayer lid).
Another solution has been proposed which consists in pre-perforating a hole in the lid and covering it with an easily removable adhesive element. But this system is not really satisfactory either where the preservation of certain products is concerned.
A system using a peelable lid has been very favorably received by the producers as well as by the consumers. Normally associated with a thermo-shaped container production installation, this system has led to a reliable and inexpensive opening system.
Nonetheless, there are products for which this last system cannot be used, in particular for long-term packagings or packagings of a sterile nature which require perfect tightness at the level of the lid, this being only obtained by auto-welding sealings which therefore are not peelable.
Lid-opening devices are also known from French Pat. No. 2 241 466 using piercing tabs by leverage, but on the one hand, the tabs are bonded flat directly on the lids, which are made of relatively rigid plastic material, and on the other hand said opening devices are necessarily associated with a lid comprising frangible score lines and make the opening more by shearing the lines than by really piercing the lid. These known devices have the disadvantage of either not giving to the tab a definite articulation, in which case the device works badly or else the tab can even detach itself from the lid, or requiring the presence on the lid proper of means independent of the tab and giving the latter a definite articulation. But, in this latter case, the production of these extra means--when it is possible--complicates and slows up the production line of the sealed containers; in addition, this makes it necessary afterwards to place the tabs in a very accurate position predetermined in relation to said extra means, which is not always easy and compatible with a high rate of production.